摘要:

A study is made of the guiding‐center motion of charged particles in a collisionless magnetoplasma in the standard paraxial limit, with finite‐orbit ordering. As a preliminary, a simple one‐fluid representation of the macroscopic plasma motion is set up, and the guiding‐center equations are then referred to a Lagrangian coordinate network comoving with the representative fluid. They are then found to split themselves off from the fluid equations as an autonomous subsystem. It is concluded that the fluid motion (or the network motion) has no effect on the guiding‐center trajectories relative to the network.

ISSN:0031-9171    

DOI:10.1063/1.865114

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Two‐dimensional, hydrodynamic turbulence, and the transport of enstrophy by this turbulence from large spatial scales to small spatial scales, is considered. This fluid is taken as slightly ionized, with a small number of ions in equilibrium with it. These ions produce a fluctuating magnetic field that induces a fluctuating electric field, either or both of which alter the distribution function of the electrons present. Considering a cold‐electron plasma, it is found that turbulence can heat the electrons, increase their Langmuir frequency and decrease the Landau damping.

ISSN:0031-9171    

DOI:10.1063/1.865115

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The two‐dimensional Fokker–Planck equation with strong quasilinear diffusion on the tail of the electron distribution function is solved analytically and numerically. The quasilinear diffusion is taken to be parallel to the confining magnetic field of the plasma, as is appropriate for lower‐hybrid current drive. The radio frequency fields that produce this quasilinear diffusion are assumed to be imposed by external sources. It is found that an appreciable broadening of the resonant plateau in the direction perpendicular to the toroidal magnetic field leads to more particles carrying the current. As a result both the current (J) and the power dissipated (Pd) are substantially enhanced, compared with the predictions of one‐dimensional theory. The figure of meritJ/Pdis three times larger than the one found from the one‐dimensional theory.

ISSN:0031-9171    

DOI:10.1063/1.865116

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Electrostatic properties of density gradient drift waves (the universal mode) in a sheared magnetic field are studied using a two‐and‐one‐half dimensional (2 1/2 ‐D) particle code. For the case of a single rational surface, the drift waves are found to be stable with an eigenmode structure that matches the linear theoretical prediction as long as the ion resonance layer is well within the system. This applies to both even and odd parity modes with respect to the rational surface. The dependence on various parameters such as the shear length is examined.

ISSN:0031-9171    

DOI:10.1063/1.865117

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A calculation of the quasilinear transport and heating of plasma particles and diffusion of particle energy is presented, emphasizing the resonant interaction of plasma particles with waves in the magnetic drift frequency range. Substantial transport can occur for relatively small wave field amplitudes in a number of applications involving tandem mirrors and ELMO Bumpy Toruses (EBT), e.g., pumping of thermal barriers in tandems and profile control in EBT’s. The diffusion is selective and can cause preferential transport of a particular charge or energy component, and can even be inward in some cases.

ISSN:0031-9171    

DOI:10.1063/1.865118

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The linearized resistive magnetohydrodynamic (MHD) equations have been solved analytically in a large‐aspect‐ratio toroidal plasma to obtain a dispersion relation for resistive ballooning modes. The calculation is limited to values of &bgr;=8&pgr;nT/B2below the threshold for ideal ballooning modes. The dispersion relation yields a universal curve which can be used to determine mode stability as a function of the plasma parameters. Because of the strong stabilizing influence of plasma compressibility, resistive‐ballooning modes are only unstable in tokamaks which are either quite cold or are very close to the ideal threshold.

ISSN:0031-9171    

DOI:10.1063/1.865119

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An experiment is described where an anomalously rapid current penetration is correlated with the appearance of strong fluctuations measured with a forward laser scattering technique. In this experiment, the current of a magnetized plasma column (5 eV, 1021m−3) is reversed linearly on a time scale (&mgr;sec) much shorter than the classical time for current penetration toward the center of the column. Strong skin currents are observed to develop followed by a rapid current transport phase. The anomaly level of the current penetration is inferred from a comparison with numerical simulations. Simultaneously with the appearance of strong skin currents, we observe the onset of a large fluctuation level (n˜e/ne∼1%) which persists for the duration of the anomalous current transport phase. The main contribution is from broadband fluctuations at low frequencies (a few MHz) and long wavelengths (a few mm). The nature of the fluctuations is not clear although a low level of ion‐acoustic turbulence appears to be involved.

ISSN:0031-9171    

DOI:10.1063/1.865120

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The importance of error magnetic fields is that, if large enough, they cause the destruction of magnetic surfaces. In this paper error fields in a cylindrical plasma are described by nonlinear tearing mode theory, which deals with plasma equilibria having concentrated currents flowing along closed magnetic field lines. Because of the small spatial scale of the current distribution, resistive diffusion is significant even for small resistivity and, in certain cases, causes instability. An energy principle exists and is discussed. This conceptual framework is used in a study of the stability of zero pressure equilibria toward spontaneous generation of error fields, relevant for the reversed field pinch program. Cylindrical Ohmic states are shown to be extremely unstable. Relaxed states (having flattened current profiles) have much better stability. Both completely relaxed states of the Taylor type and partially relaxed Robinson‐type states are studied. A new class of metal–liner stabilized profiles is found, which offers one explanation for the apparent stability observed in experiments with distant conducting shells. The possibility that relaxed states have weakly stochastic magnetic field lines is discussed.

ISSN:0031-9171    

DOI:10.1063/1.865121

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A model is presented which describes the neutral density transients in gaseous discharges. It is shown that the duration of the initial density transient is governed by the speed of sound in the gas in which the discharge is produced. The development of the gas‐flow velocity pattern in the discharge tube is a consequence of the interplay between three competing volume forces: (a) the driving volume force, which is generated by the interaction of the charged particles with the neutral particles, (b) the viscosity force, and (c) the neutral pressure gradient force. The influence of the geometry of the discharge tube on the neutral particle density transients is also discussed. The initial neutral particle density transient is believed to be the origin of acoustic resonances observed in rf‐excited gaseous discharges.

ISSN:0031-9171    

DOI:10.1063/1.865122

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Nonlinear two‐ and three‐fluid equations are written for the time evolution of the perturbed electrostatic potential, densities, vector potential, and parallel ion motion of collisional and trapped electron plasmas in tokamak geometry. The nonlinear terms arise from theE˜×B0convection (d˜/dt=∂/∂t+v˜E ⋅ ∇⊥) and magnetic flutter [∇˜∥=∇∥+(B⊥/B0) ⋅ ∇⊥]. Simplified two‐dimensional (k⊥) mode coupling simulations with a fixed average parallel wavenumber (k∥=1/Rq) and curvature drift [&ohgr;g=(Ln/R)&ohgr;*] characteristic of outward ballooning are performed. Homogeneous stationary turbulent states of the dissipative drift and interchange modes from 0≤&bgr;<&bgr;critfor both the collisional and trapped electron plasmas are obtained. Transport coefficients associated withE×Band magnetic motions are calculated. The problem of simulating plasmas with high viscous Reynolds number is treated with an absorbing mantle at the largest wavenumbers. The results are summarized by comparison to simple mixing length rules:n˜/n0∼1/k⊥Ln, B˜/B0∼(&bgr;/2) ⋅ q ⋅ n˜/n0, DE∼&ggr;/k2⊥.

ISSN:0031-9171    

DOI:10.1063/1.865123

出版商:AIP    

年代:1985

数据来源: AIP